Apparatus for the continuous adjustment of the reflux ratio of a distillation column

ABSTRACT

The reflux ratio of an industrial distillation column can be accurately varied in a programmed manner by passing the distillate through a reflux ratio regulator having an elongate housing having an elongate fluid inlet in a side wall thereof, a partition fitted axially in the housing perpendicular to the axis of the inlet and movable axially between the ends of the inlet; a first fluid outlet positioned on one side of the partition; a second fluid outlet positioned on the other side of the partition; means for varying the position of the partition along the inlet during the distillation, so that the partition divides the stream of distillate entering the housing in a varying ratio into two streams, one being withdrawn as distillate and the other being returned as reflux; and, optionally, a liquid stream divider downstream of the reflux ratio regulator comprising an elongate housing having in the side walls thereof a fluid inlet connected to one of the fluid outlets of the reflux ratio regulator and two fluid outlets, one connected to the head of the distillation column and one to means for collecting the product; a weir with a plurality of overflow indents in its upper edge positioned axially in said housing between the fluid inlet and the fluid outlets; and a liquid stream dividing wall mounted transversely in said housing and mounted perpendicularly to the weir, so that the stream of liquid flowing over the weir is divided by the dividing wall into two streams, one of which exists through the first fluid outlet and the other stream exits through the second fluid outlet.

United States Patent 51 3,670,769

Gelderblom et al. 1 June 20, 1972 [54] APPARATUS FOR THE CONTINUOUS ADJUSTMENT OF THE REFLUX RATIO ABSTRACT OF A LAT COLUMN The reflux ratio of an industrial distillation column can be ac- [72] Inventors: Horst-Dieter Gelderblom Sindorf' Mancurately vafied in a Pmgfammed manner by passing the dism' red Morsdorf xolmweidenpesc both late through a reflux ratio regulator having an elongate housing having an elongate fluid inlet in a side wall thereof, a partition fitted axially in the housing perpendicular to the axis of [73] Assignee: Chemlebau Dr. A. Zieren GmbH 8: Co. the inlet and movable axially between the ends of the inlet; a K.G., Koln, Germany first fluid outlet positioned on one side of the partition; a

second fluid outlet positioned on the other side of the parti- [22] filed: June 1970 tion; means for varying the position of the partition along the 21 l N 51,295 inlet during the distillation, so that the partition divides the stream of distillate entering the housing in a varying ratio into two streams, one being withdrawn as distillate and the other of Germany [30] Foreign Application Data being returned as reflux; and, optionally, a liquid stream di- June 30, 1969 Germany ..P 19 33 056.4 dWnstream reflux mPYisin8 an elongate housing having in the side walls thereof a fluid inlet I 52] n 137/610 connected to one of the fluid outlets of the reflux ratio regula- [511 Int mF16k51/00 tor and two fluid outlets, one connected to the head of the [58] Field of Search 1 37/610 625.48 262 266 and means meeting product; a weir with a plurality of overflow indents in its upper edge positioned axially in said housing between the fluid inlet [56] References Cited and the fluid outlets; and a liquid stream dividing wall UNITED STATES PATENTS mounted transversely in said housing and mounted perpendicularly to the weir, so that the stream of liquid flowing over 3,208,468 9/1965 Hansen 1 37/266 the is divided by the dividing wall into two streams, one of 3,428,083 2/1969 Fish 1 37/262 X whieh exists through the first fl id Oufle and the other stream exits through the second fluid outlet. Primary Examiner-Henry T. Klmksiek Attorney-Millen, Raptes & White 1 1 Claims, 6 Drawing Figures 1 u s tL PATENTEDmao m2 3.670.769

sum 10: 2

INVENTORS HORST-DIETER GELDERBLOM MANFRED MORSDORF PATENTEDJIJXZO m2 3. s70 769 SHEET 2 OF 2 INVENTORS HORST-DIETER GELDERBLOM MANFRED MORSDORF ATTORNEYS APPARATUS FOR THE CONTINUOUS ADJUSTMENT OF THE REFLUX RATIO OF A DISTILLATION COLUMN This invention relates to an apparatus for the continuous adjustment of the reflux ratio of an industrial distillation column.

During the operation of industrial distillation columns, in most cases, to achieve the desired separating efi'ect it is necessary to allow a more or less large portion of the liquid collected at the head of the column to flow back into the column and to withdraw only the remainder as the product. The quotient of reflux stream and distillation stream is called the reflux ratio and is an important product entity for distillation plants. The specific reflux ratio which is selected depends on the particular distillation problem involved, i.e., on the properties and the desired purity of the substances to be separated. In order to obtain the desired fractionation, it is frequently necessary in plant operation to vary the reflux ratio over wide limits, depending on whether the boiling points of the sub stances to be separated differ greatly or only little. For example, in the discontinuous rectification of crude products containing more volatile impurities, e.g., crude phthalic anhydride, it is important to separate the more volatile impurities together with as little of the main product as possible. To do so, it is necessary first to conduct the distillation with a high reflux ratio. The reflux ratio is thereafter greatly reduced for the distillation of the main product since a smaller fractionab ing effect is sufficient after the separation of the more volatile impurities and a higher reflux ratio would entail an unnecessarily high heat requirement. In this type of distillation, the reflux ratio must be varied during the course of the distillation in accordance with a specific program adapted to the special separation problem, so that an optimum separation is achieved with minimum heat consumption.

OBJECTS OF THE INVENTION It is an object of the present invention to provide an apparatus by which the reflux ratio of a distillation column can be continuously adjusted within wide limits, independently of the available differential pressure. It is another object to provide such an apparatus which permits very accurate adjustment of the reflux ratio, even at high reflux rations. It is a further object to provide such an apparatus which is constructed so as to be connected to a remote control, a program control device, and/or a control circuit. Other objects will be apparent to those skilled in the art to which this invention pertains.

SUMMARY OF THE INVENTION In accordance with the invention, there is provided an elongate housing with an elongate fluid inlet in a side wall thereof; a partition axially fitted in the housing perpendicular to the axis of the inlet and movable axially between the ends of the inlet; a first fluid outlet positioned on one side of the partition; a second fluid outlet positioned on the other side of the partition; and means for positioning the partition at any selected position in its path of travel, whereby a stream of fluid flowing through the inlet into the housing is divided in any selected ratio into two streams flowing out of the housing through the first and second outlets.

DETAILED DISCUSSION The housing suitably is cylindrical with the displaceable partition serving as the divider for the condensate being fed from the condenser. In operation, the condensate enters through the oblong axially parallel inlet with a quantitative distribution which is equal along the opening in the housing forming the inlet. The partition can be shifted during the distillation to achieve the desired ratio of division of condensate into two streams. Depending on the position of the partition, along the mouth of the inlet, the condensate inlet opening is subdivided in a specific ratio so that the amount of condensate flowing on both sides of the partition into the housing is likewise divided in the same ratio. The two outlet openings of the housing serve to discharge the two divided streams from the housing, one of which is recycled as reflux to the column and the other is withdrawn as distillate. The two discharge openings forming the fluid outlets are disposed at the housing outside range of displacement of the partition so that even in its extreme position of travel there is a discharge opening on each side of the partition. This insures that in any position of the partition, i.e., at any ratio of division of the liquid, a portion of the condensate stream is discharged through each opening forming the fluid outlet. The inlet opening of'the housing is preferably interposed between the collecting plate of the column in a manner such that all-of the condensate passes through the apparatus of this invention.

Because the partition can be positioned at any point along the fluid inlet, any desired ratio of division of the condensate into distillate and reflux can be obtained. In difficult separation problems, extreme reflux ratios of about 3021 to :1 often must be maintained. In such cases, i.e., the partition would, for this ratio of division, be disposed only a very small distance from the end of the inlet opening for the condensate, which permits most of the condensate to be returned as reflux. Ordinarily, the setting of such a high reflux ratio would result in considerably inaccuracy. To obtain an accurate reflux ratio, even in case of such extreme ratios, the discharge opening for the product to be withdrawn preferably is connected to a further liquid stream divider wherein the smaller of the two streams of liquid is once again divided. By recycling, in this stepwise division, the larger partial stream obtained by the second division along with the larger partial stream obtained by the first division, back to the distillation column and withdrawing only the smaller partial stream of the second division as the product, high reflux ratio is attained without the movable partition of the apparatus being disposed very close to one end of the inlet opening for the condensate, which causes a considerable inaccuracy in the reflux ratio.

According to a special embodiment of the invention, the partition is rigidly mounted in a sleeve-like movable piston. In the wall of this piston is provided an opening which is divided by the partition and which communicates on both sides of the partition with the condensate feed opening of the housing forming the fluid inlet and, on respective sides of the partition, with the first and second outlet openings, respectively of the housing. With the partition rigidly mounted in a piston slidably mounted in the cylindrical housing, exact positioning of the partition with respect to the inlet opening for the condensate is pomible. Moreover, by attaching an externally adjustable positioning rod to the sleeve, a satisfactory heat-conductive connection can be established from the operating rod via the sleeve to the partition.

The fluid inlet opening of the housing intended for feeding the condensate liquid to the metering apparatus is preferably rectangular in shape with a horizontal lower edge. A thusshaped and thus-positioned fluid inlet ensures a flow of condensate which is uniformly distributed over the length of the opening. Thus, the position of the partition determines the ratio of division of the length of the opening, which in turn determines the ratio of the division of condensate flowing through the opening into the housing into a first stream flowing out of the apparatus through the first outlet and a second stream flowing out of the apparatus through the second outlet.

According to a preferred embodiment of the invention, the partition is connected, by connecting means, with the piston of a servomotor, which latter is preferably actuated hydraulically. The servomotor can be part of a control circuit which regulates the reflux to the column in the desired manner. By combination with a program control device, it is also possible to vary the reflux ratio in accordance with a program adapted to the specific separating task. Thus, for example, in the discontinuous distillative purification of crude phthalic anhydride, it is possible to reduce the reflux ratio from initially high values to the value required for the distillation of pure phthalic anhydride. By operating the apparatus with a servomotor, it is also possible to monitor the setting of the apparatus of this invention at any moment at a central control point along with other control variables required in the distillation operation.

In a preferred embodiment, the connecting means between the adjustable partition in the housing and the piston of the servomotor contains a heatable slide bar extended through the end wall of the housing. Heating of the apparatus of this invention is necessary in the distillation of high-melting products. For example, during the distillation of phthalic anhydride, the condensate passing through the apparatus of this invention must no cool down to below l3l C., since otherwise solid deposits occur which can cause disturbances in the distillation operation. In order to ensure safe operation in such cases, a heatable slide bar is mounted to the sleeve in which the partition is mounted. This slide bar is preferably a hollow tubular rod which is heated interiorly, e.g., with steam at 7 atmospheres gauge. By heating the slide bar, deposition of a high-melting condensate on the slide bar within the housing with resulting inhibition of the mobility of the bar in the packing gland is avoided.

Provision is preferably also made so that the connecting means between the sleeve or piston slidably mounted in the cylindrical housing and the servomotor driving means for the sleeve is at least partially flexible. Such a flexible connecting means makes it possible to arrange the regulating apparatus for the reflux ratio according to the invention and the servomotor associated therewith in such a mutual relation that the axes thereof form with each other an angle other than 180, e.g., about 90. It is thus possible to mount these devices in a space-saving manner immediately at the wall of the column head.

In a further embodiment of this invention, the liquid quantity divider optionally connected to the second outlet opening of the apparatus of this invention, consists of a housing with a single feed opening or inlet and two discharge openings or outlets for the two streams of liquid formed therein with a weir, mounted between the feed opening and the discharge openings having several horizontally arranged overflow points or spillways which exhibit equal overflow cross sections. A wall mounted in the housing downstream of the weir separates a portion of the overflow liquid and one of the discharge openings from the other portion of the overflow liquid and the other discharge opening. As stated above, the setting of a large reflux ratio, e.g., over 50:1, solely with the variably adjustable apparatus of this invention, entails an error which sometimes is too great for the proper operation of the distillation column. In such cases, the second outlet opening of the cylindrical housing is connected to the above-described liquid quantity divider which divides the partial stream of condensate from the second outlet opening in a fixed volume ratio. One of the streams of condensate obtained by this division is then returned to the head of the column along with the stream of condensate flowing from the first discharge opening of the reflux ratio adjusting apparatus of this invention. Only the other partial stream exiting from the liquid quantity divider is withdrawn as the product. A three-way valve is disposed at the connecting conduit between the second discharge opening of the adjusting apparatus of this invention and the feed opening of the liquid quantity divider, which valve can be used to bypass the quantity divider and conduct the condensate exiting from the adjusting apparatus of this invention directly into the product receiver. At high reflux ratios, the condensate thus is divided twice, and, when the reflux ratio is reduced, the liquid quantity divider is finally by-passed and only a single stream division is conducted by the adjusting apparatus in the desired ratio.

Preferably the wall in the liquid quantity divider downstream of the weir is provided with n overflow points, one overflow point is positioned on the weir on one side of the wall, and 11-1 overflow points are provided on the other side of the wall. For example, if the weir has eight overflow points, the liquid stream entering the liquid quantity quantity divider is divided in a volume ratio of 7: l with only one part thereof being withdrawn as the product. For example, if the desired reflux ratio is 70:1, then the ratio adjusting apparatus of this invention is adjusted to divide the liquid stream in a ratio of 63:8 and the eight parts are divided in the quantity divider connected thereafter in the ratio of 7:1. The 63 7 parts by volume are recycled to the column and the one part by volume flows to the product receiver. Preferably at least the lower portion of the overflow points is designed with a cross section which tapers downwardly with a wedgelike manner. The pointed shape ensures that even in case of a small throughput of liquid, a uniform distribution of the liquid over all overflow points is obtained, and thus an accurate maintenance of the ratio of division of the volume of condensate flowing through the liquid quantity divider is attained.

The apparatus of this invention will be explained in greater detail with reference to the drawings, in which:

FIG. 1 is a schematic longitudinal sectional view of the apparatus of this invention for the continuous adjustment of the reflux ratio;

FIG. 2 is a cross section along line 11-" of FIG. 1;

FIG. 3 is a schematic longitudinal section through the quantity divider connected thereafter downstream to the apparatus shown in FIG. 1;

FIG. 4 is a cross section along line lV--IV of FIG. 3;

FIG. 5 is a preferred embodiment of the apparatus of this invention connected to a servomotor and a liquid quantity divider and mounted on a distillation column; and

FIG. 6 is a schematic representation of connections employed in conjunction with the apparatus of this invention.

As shown in FIGS. 1 and 2, the apparatus A of this invention is a cylindrical housing 1 and a sleeve-shaped slide or piston S slidably mounted therein. Positioned approximately in the middle of a sidewall of cylindrical housing 1 is an elongated fluid inlet opening 2 for the liquid condensate being fed from the collecting plate of the distillation column (not shown). Two fluid outlet openings 3 and 4 are provided in housing 1, ositioned on an end wall and the bottom wall, respectively, of housing 1. Piston 5 contains a partition 6 rigidly mounted perpendicularly to the axis of housing 1 and the piston S, and which is displaceable together with piston 5 at least along the entire inlet opening 2. A slide bar or hollow connecting rod 7 is axially mounted to tubular slide 5 and extends outside housing 1 through the end wall or lid 10 thereof opposite the end wall containing outlet 3 and is sealed with respect to lid 10 by means of a conventional seal (not shown). Slide bar 7 has a hollow bore 8 and carries a distributing head 9 at the end thereof which extends outside housing 1. Distributing head 9 has bores 11 therein providing internal fluid communication with bore 8 of slide bar 7 and 12 for the introduction of steam and discharge of condensed water, respectively. Slide 5 with slide bar 7 and distributor element 9 are connected by a flexible drive shaft 13 to a reciprocating driving means (44), by means of which the slide 5 and partition 6 can be moved axially on housing 1. The slide or piston 5 has three openings in its side walls. The opening 41 is elongate and extends on both sides of the partition 6 and receives the reflux from the inlet 2. The posifion of the slide with respect to the inlet will determine the amount of reflux delivered to the opposite sides of the partition. The openings 42 and 43 are located on opposite sides of the partition 6 and are at a generally lower level than the opening 41. The opening 42 is located to direct fluid from the inlet 2 to the outlet 4 and the opening 43 is located to direct a portion of the reflux from the inlet 2 to the outlet 3.

The liquid quantity divider B, illustrated in FIGS. 3 and 4 has a cylindrical housing 14 with a condensate feed opening or fluid inlet 15 therein positioned perpendicular to the axis of housing 14 for receiving the stream of condensate from the liquid quantity divider shown in FIGS. 1 and 2, and two outlet openings of fluid outlets l6 and 17 in the wall of housing 14 opposite the wall containing feed inlet opening 15 for discharging the divided streams of condensate. In housing 14, between the inlet opening 15 and outlet openings 16 and 17, is positioned an axially extending vertical barrier or weir 18 having a plurality of overflow apertures 19 in its upper edge. A dividing wall or partition 20 is positioned between the first and second overflow notches 19 and between outlet openings 16 and 17, on the downstream side of weir 18 and perpendicular to the axis of housing 1. The dividing wall or partition 20 may be mounted on a sleeve similar to the sleeve 5 of FIG. 1. Mounted on the top of cylindrical housing 14 is a pressure equalizing stand pipe 21, which latter can be in communication with the head of the distillation column.

Referring to FIGS. 5 and 6, mounted on the head of distillation column 22 is a condenser 23 which is connected via conduit 24, to the reflux ratio adjusting apparatus A of this invention, whose slide bar 7 is connected, via flexible drive shaft 13, to a servomotor 44. One of the outlets of apparatus A is connected via condensate recycling conduit 25 to the column 22, and the other outlet is connected through three-way valve 34, via conduit 26, to quantity divider apparatus B, and to receiver 36, via conduit 35. Apparatus B is connected via conduit 27 to column 22, via conduit 28 to product receiver 29, and via conduit 32 to product receiver 33. Conduits 27 and 28 having shut-off valves 30 and 31, respectively, therein. Adjusting apparatus A and liquid quantity divider B are connected, via pressure equalizing conduits 37 and 38, respectively, to the head of condenser 22. Pumps 37, 38, 39, and 40 are provided on the conduits 27, 28, 32 and 35 to move the fluids to their destinations.

In operation, as a result of partition 6 being positioned in front of opening 2, the stream of condensate entering housing 1 is divided into two streams, one flowing into outlet 3 and one flowing into outlet 4. With partition 6 in the position shown in FIG. 1, approximately one-fourth of the volume of condensate flows axially along housing 1 toward the right and through the discharge opening 3, and approximately three-fourths of the volume of condensate passes downwardly through the discharge opening 4. Recycling the condensate drained through opening 4 to column 22 via conduit 25 and withdrawing the condensate drained through opening 3 via conduit 35 as the product, operates the apparatus at a reflux ratio of about 3:1. To obtain a substantially higher reflux ratio, the condensate discharged through opening 3 is passed via conduit 26 to liquid divider B, where the stream is divided once more.

As shown in F165. 3 and 4, dividing wall 20 provides a liquid barrier which permits only the liquid from the first overflow notch 19, viz the overflow disposed in FIG. 3 on the extreme righthand side, to exit through outlet opening 17, whereas the liquid condensate from the remainder of overflow notches 19 is discharged through outlet opening 16. Ifweir 18 contains eight overflow apertures 19, quantity divider B will thus divide the liquid condensate entering through opening in the ratio of 7:l. Recycling the larger stream to column 22 along with the larger stream from adjusting apparatus A thereby provides an accurate high reflux ratio.

if the column 22 is to be first operated at a selected high reflux ratio, which can be obtained in A only approximately, the larger partial stream exiting from apparatus A is allowed to flow to quantity divider apparatus via conduit 26. Ifduring the course of the distillation, the reflux ratio is changed by the servomotor 44, so that a different quality condensate is obtained, the resultant condensate can optionally be collected in the receiver 33 by closing valve 30 and opening valve 31. Finally, if the main product is to be distilled over at a low reflux ratio, the product can be conducted directly into the receiver 36 via conduit 35, by shifting three-way valve 34, thereby by-passing apparatus B.

The invention is not limited to the illustrated embodiment;

numerous modifications, self-evident to a person skilled in the art, are possible, all of which are within the scope of protection of the following claims.

What is claimed is:

1. Apparatus for regulating the reflux ratio of a distillation column comprising an elongate housing with an elongate fluid inlet in a side wall thereof and extendin in the longitudinal direction thereof; a partition axially fitte in said housing and movable axially between the ends of said inlet; a first fluid outlet positioned on one side of said partition; a second fluid outlet positioned on the other side of said partition; and means for axially moving and positioning said partition at any selected position in its path of travel.

2. Apparatus according to claim 1 wherein said fluid inlet is rectangularly shaped with a horizontal lower edge.

3. Apparatus according to claim 1 wherein said means for positioning said partition comprises a servomotor connected to said partition.

4. Apparatus to claim 3 wherein said servomotor is connected to said partition by connecting means which comprise a hollow slide bar which extends through said end wall of said housing the hollow bar providing means to introduce a heating medium.

5. Apparatus according to claim 3 wherein said servomotor is connected to said partition by connecting means, at least a portion of which is flexible.

6. Apparatus according to claim 1 in which the housing is cylindrical and there is a sleeve-shaped slide slidable axially of said housing within the housing, said partition being mounted on said slide perpendicularly to the axis of the housing, said slide having a first opening in a side wall thereof adjacent to the inlet to the housing and extending axially on both sides of said partition so that said first opening is subdivided by said partition, and a second opening in a wall of said slide and displaced from the first opening and adjacent the first fluid outlet, so that the slide provides communication between said fluid inlet and said first fluid outlet, and a third opening in a wall of said slide on the opposite side of the partition and displaced from the inlet and adjacent the second fluid outlet so that the side provides communication between said fluid inlet and second fluid outlet.

7. Apparatus according to claim 1 in which the elongated fluid inlet in the side wall includes a weir positioned axially of said housing adjacent said partition, said weir having in its upper edge a plurality of horizontally arranged overflow apertures of equal cross sections.

8. Apparatus according to claim 7, wherein at least the lower portion of said overflow indents are wedge-shaped notches which taper downwardly.

9. Apparatus according to claim 7 in which there is a sleeveshaped slide slidable axially of said housing, said partition being mounted on said slide and perpendicular to the axis, said slide having a first opening in a side wall thereof, which is subdivided by said partition, and a first and second opening in said slide on opposite sides of the partition so that the slide provides communication for the reflux discharged from said weir to the first and second outlets in said housing.

10. Apparatus according to claim 9, wherein said means for positioning said partition comprises a servomotor connected to said partition.

11. Apparatus according to claim 10, wherein said servomotor is connected to said partition by connecting means which comprise a hollow slide bar which extends through said end wall of said housing the hollow bar providing means to introduce a heating medium. 

1. Apparatus for regulating the reflux ratio of a distillation column comprising an elongate housing with an elongate fluid inlet in a side wall thereof and extending in the longitudinal direction thereof; a partition axially fitted in said housing and movable axially between the ends of said inlet; a first fluid outlet positioned on one side of said partition; a second fluid outlet positioned on the other side of said partition; and means for axially moving and positioning said partition at any selected position in its path of travel.
 2. Apparatus according To claim 1 wherein said fluid inlet is rectangularly shaped with a horizontal lower edge.
 3. Apparatus according to claim 1 wherein said means for positioning said partition comprises a servomotor connected to said partition.
 4. Apparatus to claim 3 wherein said servomotor is connected to said partition by connecting means which comprise a hollow slide bar which extends through said end wall of said housing the hollow bar providing means to introduce a heating medium.
 5. Apparatus according to claim 3 wherein said servomotor is connected to said partition by connecting means, at least a portion of which is flexible.
 6. Apparatus according to claim 1 in which the housing is cylindrical and there is a sleeve-shaped slide slidable axially of said housing within the housing, said partition being mounted on said slide perpendicularly to the axis of the housing, said slide having a first opening in a side wall thereof adjacent to the inlet to the housing and extending axially on both sides of said partition so that said first opening is subdivided by said partition, and a second opening in a wall of said slide and displaced from the first opening and adjacent the first fluid outlet, so that the slide provides communication between said fluid inlet and said first fluid outlet, and a third opening in a wall of said slide on the opposite side of the partition and displaced from the inlet and adjacent the second fluid outlet so that the side provides communication between said fluid inlet and second fluid outlet.
 7. Apparatus according to claim 1 in which the elongated fluid inlet in the side wall includes a weir positioned axially of said housing adjacent said partition, said weir having in its upper edge a plurality of horizontally arranged overflow apertures of equal cross sections.
 8. Apparatus according to claim 7, wherein at least the lower portion of said overflow indents are wedge-shaped notches which taper downwardly.
 9. Apparatus according to claim 7 in which there is a sleeve-shaped slide slidable axially of said housing, said partition being mounted on said slide and perpendicular to the axis, said slide having a first opening in a side wall thereof, which is subdivided by said partition, and a first and second opening in said slide on opposite sides of the partition so that the slide provides communication for the reflux discharged from said weir to the first and second outlets in said housing.
 10. Apparatus according to claim 9, wherein said means for positioning said partition comprises a servomotor connected to said partition.
 11. Apparatus according to claim 10, wherein said servomotor is connected to said partition by connecting means which comprise a hollow slide bar which extends through said end wall of said housing the hollow bar providing means to introduce a heating medium. 